1. Field of the Invention
The present invention relates to a transfer belt for electrophotography and an image-forming apparatus.
2. Description of the Related Art
In an image-forming apparatus in which an electrophotographic system is adopted, an intermediate transfer belt and a direct transfer belt, used for transferring a toner image, are adopted. A conductive agent such as carbon is blended in such a transfer belt and the conductive property of the transfer belt is set within a semiconductor area.
It has been known that a polyphenylene sulfide resin (hereinafter, referred to simply as a “PPS resin”), which has superior characteristics as an engineering plastic material, from the viewpoints of heat resistance, flame resistance and rigidity, is preferably used as a resin forming the transfer belt. In general, the transfer belt is manufactured into a seamless annular shape through processes in which, after a resin composition containing a PPS resin and carbon has been extrusion-molded by a molding machine equipped with an annular metal mold die, the resulting molded product is cooled.
However, the PPS resin is not necessarily superior in the dispersing property of carbon, resulting in a problem in that upon extrusion-molding, the dispersed state of carbon fluctuates to cause nonuniformity in the conductive property. For example, during the molding process, the seamless annular shaped transfer belt tends to have an extremely high rate of content of the conductive agent within an area inside an annular metal mold die where fused resin portions are joined with each other in comparison with the other areas, with the result that the resistivity fluctuates greatly in the circumferential direction. When the resistivity fluctuates in the circumferential direction in the transfer belt, hollow defects and scattering occur.
With respect to the method for improving toughness of a non-reinforced PPS material containing no reinforcing agent such as glass fibers, a PPS resin composition that is allowed to contain a polyamide resin or the like has been known (JP-B No. 59-1422, JP-A No. 53-69255, JP-A No. 6-49356). Upon blending the PPS resin with polyamide, the two components are hardly made compatible with each other; however, it has been reported that 4, 6-nylon is compatible therewith at a high temperature of 300° C. or more (J. MACROMOL. SCI. PHYS., B41(3), 407-418(2002), Jung-Bum An, Takeshi Suzuki, Toshiaki Ougizawa, Takeshi Inoue, Kenji Mitamura and Kazuo Kawanishi). An oxidized and crosslinked PPS resin that is superior in mechanical strength has been reported (JP-A No. 9-291213, JP-A No. 62-197422).